Steering system for a marine vessel

ABSTRACT

A method and a system for improving the fuel efficiency by controlling the steering system of a marine vessel. In the method the steering system is configured to acquire data related to the fuel efficiency by changing the orientations of steering devices without changing the steering angle of the marine vessel. The acquired data is modeled statistically and an optimum value can be determined from the model. The optimum value is then used for actuating the steering devices to the optimum angle.

FIELD OF THE INVENTION

The invention relates to the controlling of the steering system of a marine vessel.

BACKGROUND OF THE INVENTION

Steering rudders are a traditional way of controlling the movement of marine vessels. Smaller vessels may have only one rudder but bigger vessels have usually two or more rudders that are located after propellers causing the propulsion that moves the vessel. Although the rudders are still widely used they are often replaced by azimuth thrusters. The azimuth thruster is a configuration of ship propellers placed in pods that can be rotated in any horizontal direction. In the most typical configuration there are two thrusters located in the stern of the ship; however, other configurations also exist.

A common nominator for both of these steering methods is that the actual steering angle is a resultant angle of the orientation of each of the steering devices. In the most common configuration of two steering devices the angle between these two steering devices is called a toe angle. FIG. 1 discloses a block diagram of a configuration of two azimuth thrusters at the stern of a marine vessel for explaining the toe angle. In FIG. 1 αSB is the orientation of the thruster in the starboard side of the vessel. αPS is the orientation of the thruster in the portside of the vessel. The steering angle and the toe angle can be computed from these two orientations. The steering angle α is ½(αSB+αPS) and the toe angle Δα is αSB−αPS. Thus, if αSB=10° αPS=−3°, the steering angle is 3,5° and the toe angle is 13°. Thus, for example, when the steering angle of a vessel is 0, the toe angle can be 10 degrees meaning that the steering devices have an angle of −5 and 5 degrees respectively, and so on.

It is known that the toe angle has a significant influence on the fuel efficiency. The optimal toe angle depends on the shape of the hull and a plurality of different variables such as the weather conditions, advance speed, drift, trim, draft and similar factors affecting the wake field. Traditionally, this optimization is done during sea trials or during commissioning of the vessel. The data is collected, for example, during sea trials, and then after analysis an optimum is selected. The traditional way for selecting the optimum is to minimize the torque actuating the steering devices. This is done by a sequence of independent measurements, and the optimum value is then determined from the measurement results. The vessel is typically arranged to maintain this predetermined optimum value when the ship is in the sea mode. The drawback of the solution described above is that it does not take changing conditions, such as weather and water temperature, into account. As the toe angle has also a significant influence on the steering of the vessel, the predetermined optimum is not typically maintained when the ship is in the maneuvering mode. This happens typically only when the vessel is maneuvered during arrival or departure.

U.S. Pat. No. 7,389,165 discloses a control apparatus for controlling the attitude angle of a marine vessel. According to the publication the optimum attitude angle reduces the fuel consumption. However, the solution disclosed by the publication is related only to attitude angle control.

For ship owners the fuel expense of vessels is a significant cost. Thus, there is a clear need for further improvements in the fuel efficiency.

SUMMARY

The invention discloses a system and a method for optimizing the orientation of the steering devices of a marine vessel.

For better understanding of the invention the following features should be understood as defined in the following. A steering device in embodiments according to the invention is a rudder, an azimuth thruster or a similar device that can be used for changing the course of a marine vessel. All marine vessels have at least one steering device. Some vessels may have only one steering device but it is usual two or more. The steering system in embodiments according to the invention is a system comprising at least two steering devices and a means for controlling each of the steering devices. The steering system may comprise also other features that are known to a person skilled in the art of naval architecture. The present invention is applicable only in marine vessels having a steering system comprising at least two steering devices.

The orientation of a steering device should be understood so that the orientation has an effect on the course of the marine vessel while the vessel is sailing. In a steering system having more than one steering device this means that changing the orientation of only one steering device also changes the course of the marine vessel. It is important to understand that the orientation of a steering device can be changed without changing the course of the marine vessel if the change is compensated by changing the orientation of at least one other steering device.

The sea mode should be understood so that the when the marine vessel is in sea mode it typically proceeds in long cycles with a constant course and speed at open sea. This does not mean that course or speed changes are not possible but they are not effected at a fast pace. Typically, but not always, in the sea mode the ship is mainly controlled by the autopilot.

A propulsion device in the present application is a propeller of a traditional ship having rudders or an azimuth thruster, wherein the propeller is installed in the steering device, or similar device for propelling the vessel.

The present invention discloses a method for controlling a steering system of a marine vessel having at least two steering devices. In the method first data from the steering system of a marine vessel is acquired by changing the orientation of each steering device so that the steering angle of the marine vessel is maintained. Then a statistical model from said acquired data is created. From the statistical model it is possible to select optimum values for orientation of each steering device.

In an embodiment of the invention said acquired data is preprocessed before creating the statistical model. When the optimum values have been determined steering devices may are actuated according to said selected optimum values. The steering devices are actuated during the same journey in which the data was acquired so that optimum values can be used for every journey that the marine vessel makes. In an embodiment of the invention data is acquired from the steering system for a predetermined cycle. When acquiring the data the marine vessel is in the sea mode. Typically the acquired data comprises data relating to the fuel efficiency.

In an embodiment of the invention the preprocessing of acquired data further comprises filtering said acquired data, wherein said filtered data is limited to the data relating to at least one predetermined physical phenomenon. In an embodiment of the invention the statistical model is created by using at least one of the following machine learning methods: neural networks, Bayesian regression, or least squares regression.

In an embodiment of the invention the acquired data is sent to a remote server for processing. the method comprises acquiring data from the steering system of a marine vessel by changing the orientation of each steering device so that the steering angle of the marine vessel is maintained, sending said acquired data to a remote server and receiving optimum values for orientation of each steering device from said remote server. Sending of the data may be initiated already during acquiring step in order to reduce the time for the complete process. Steering devices are then actuated according to said selected optimum values during the same journey in which the data was acquired.

In an embodiment of the invention the method disclosed above is implemented as a computer program, wherein the computer program is configured to perform the method when executed in a computing device.

In an embodiment of the invention the steering system for a marine vessel comprising at least two steering devices and a controller for controlling the steering devices is configured to perform the method disclosed above. In a further embodiment the steering system comprises computing means for executing the computer program mentioned above. In a further embodiment the steering system comprises data communications means for sending and receiving data.

Typically present invention is implemented in a marine vessel, wherein the marine vessel has two steering devices that are typically rudders or azimuth thrusters.

Fuel efficiency in this application means how efficiently fuel is converted into propelling. Examples of fuel efficiency include admiralty coefficient, fuel consumed per nautical mile or similar. The primary benefit of the present invention is that the fuel efficiency of a marine vessel is improved compared to the static predetermined optimum angle as the improved fuel efficiency can be optimized in varying conditions such as weather conditions.

A further benefit of the present invention is that in passenger ships the passenger comfort can be increased when changing the course of the ship as the orientation of steering devices can be optimized to minimize the listing of the vessel while turning. In cargo ships this increases cargo security.

A further benefit of the present invention is that it reduces strain caused especially to the bearings of the steering device because the torque actuating the steering devices is reduced. This allows a longer maintenance cycle and causes cost savings when the mechanism keeping the steering device at the desired angle lasts longer.

A further benefit of the present invention is that it increases directional stability. This helps maintaining the course of the vessel and thus increases the savings in the fuel efficiency and maintenance.

A further benefit of the present invention is that all of the benefits mentioned above can be achieved for every journey of the marine vessel as the orientations of the steering devices may and should be adjusted for each journey respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and constitute a part of this specification, illustrate embodiments of the invention and together with the description help to explain the principles of the invention. In the drawings:

FIG. 1 is a block diagram of a marine vessel according to the prior art,

FIG. 2 is a flow chart of an example embodiment of the present invention,

FIG. 3 is a flow chart of an example implementation of the preprocessing step presented in FIG. 2,

FIG. 4 is a flow chart of an example implementation of the statistical modeling step presented in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

In FIG. 2 a flow chart of a method according to an example embodiment of the present invention is disclosed, wherein the fuel efficiency is optimized. The method is applied when the ship, for example a ship according to the example of FIG. 1, is in a sea mode. The first step of the method according to FIG. 2 is the data acquisition, step 20. The data is acquired by making changes in the orientations of the steering devices so that the changes do not change the steering angle of the ship. This is achieved so that when changing the toe angle of a configuration having two steering devices the changes compensate each other. Changing the toe angle may have a small effect on the course of the vessel; however, this is compensated by the autopilot. Compensations made by the autopilot are known to a person skilled in the art and do not belong to the scope of the present invention. The toe angle is varied so that a reasonable range of toe angles is tried. The range may be ship-specific and is learned during the use, for example from −20 degrees to 20 degrees. Different angles are tried, for example so that one cycle of varying covers starting from initial position to outermost position, then to innermost position and back to the initial position or vice versa. Other cycle types also exist such as sinusoid, saw tooth, or similar. The rate of the change of the toe angle within one cycle depends on the vessel as there are delays relating to, for example, the inertia of the vessel, hydrodynamic properties and measurement devices.

The number of the acquired variables is not limited, but all the data that can be collected may be collected. In addition to the toe angle information the most important variable is the fuel efficiency. Examples of direct fuel efficiency related variables are explained below. Further important fuel efficiency related variables having indirect influence on the fuel efficiency include, for example, the torque actuated to maintain the steering device in the desired position. The steering system of the ship comprises measurement tools for steering related data collection. Data related to the fuel efficiency may be measured from a plurality of systems relating to the propelling of the vessel. The variables measured in these systems include, for example, fuel flow to the engine, pressure of the turbo charger, break power of the engine, power delivered to the propeller or similar. Additional data, such as weather related data, is measured by using other meters.

In an embodiment of the invention the power is measured by using the admiralty coefficient that is known to a person skilled in the art. The admiralty coefficient is disclosed in the equation below.

$\begin{matrix} {{Ac} = \frac{\Delta^{\frac{2}{3}}v^{3}}{P}} & (1) \end{matrix}$

In the equation P is propulsion power, v is speed of the vessel and L is displacement of the vessel.

In an embodiment of the invention the fuel efficiency is simplified from the admiralty coefficient and determined as disclosed in the following equation.

$\begin{matrix} {k = \frac{P}{v^{3}}} & (2) \end{matrix}$

In the equation P is delivered power and v is speed of the vessel. The measurement is not limited to the examples mentioned above.

The fuel efficiency according to the present invention is not limited to the examples mentioned above.

Next, the data is preprocessed, step 21. The preprocessing is done in order to prepare the acquired data for statistical modeling. In the preprocessing the data is processed so that the significant data can be filtered from the acquired raw data. The preprocessing may be done in several different ways and it is important to note that the preprocessing is not required for the statistical modeling if the statistical model used is sufficiently sophisticated. However, in the embodiment disclosed in FIG. 2 it is used as it often provides good results and thus leads to a simplified statistical model. The embodiment of FIG. 3 discloses one example and explains the principles of the preprocessing according to the present invention.

The preprocessed data is then modeled statistically, step 22. The statistical model creation includes modeling the preprocessed data so that the result can be mathematically analyzed. The statistical analysis may be done by using machine learning methodologies, such as neural networks, Bayesian regression, least squares regression or similar method. The end result of the statistical model creation is a mathematical model adapted to the preprocessed data. FIG. 4 discloses an example of statistical model creation and principles of it.

From the statistical model it is possible to choose the optimum toe angle, step 23. For example, if the chosen mathematical model is analytic, the optimum can be easily selected by derivation or by using numerical methods, such as gradient descent.

Finally, the steering system is adjusted according the computed optimum toe angle, step 24. The steering adjustment may be fully automatic or just a recommendation to the crew that needs to approve the change in the toe angle.

FIG. 3 discloses an example of a preprocessing according to an embodiment of the present invention. The purpose of the preprocessing is to provide a data set that can be statistically analyzed and from which the optimum toe angle can be determined.

The preprocessing disclosed in FIG. 3 is based on the cycles as mentioned above. Each of these cycles is selected respectively, step 30. For each selected cycle an average value of fuel efficiency is computed, step 31. Then the computed averages are subtracted from fuel efficiency data of each cycle, step 32. The purpose of the preprocessing is to provide data to which it is possible to apply a statistical analysis. Thus, different preprocessing methods may be chosen for fulfilling the needs of the statistical model used.

In FIG. 4, statistical model creation is disclosed in more detail. In the example of FIG. 4 the initial data is first received, step 40. The initial data may be data that has been preprocessed according to the embodiment of FIG. 3; however, the initial data may be also data that has not been pre-processed or is preprocessed differently. Likewise, the statistical modeling of FIG. 4 is one example.

In FIG. 4, it is decided to use least squares regression as a statistical analysis method. For the statistical modeling, the actual model is typically predetermined, for example a second degree polynomial as in the following.

e(Δα)=aΔα ²+bΔα+c  (3)

Values for a, b and c can be computed by using, for example, the least squares regression, step 41, from which the values are received, step 42. The optimum angle is where the function e representing the power used is minimized. This can be solved by derivation, step 43.

$\begin{matrix} {\frac{}{{\Delta\alpha}} = {{{2a\; {\Delta\alpha}} + b} = 0}} & (4) \end{matrix}$

When we know a and b, it is possible to solve the optimum toe angle Δα from the equation (4)

The example disclosed above is for optimizing the fuel efficiency. In a further embodiment the method according to the present invention may be used for reducing listing when the ship is turning. In this embodiment a penalty function is applied instead of fuel efficiency functions (1) and (2) presented above. An example of a penalty function is disclosed below

$\begin{matrix} {k = {\frac{P}{v^{3}} + {c\; {\gamma \cdot {ROT}}}}} & (5) \end{matrix}$

-   -   wherein γ is dynamic listing of the vessel, ROT is rate of turn         and c is a predetermined coefficient. The predetermined         coefficient c defines the weight of the listing optimization in         the penalty function. As marine vessels have various reasons for         listing, the purpose of the rate of turn is to limit the         optimization to the turns of the vessel. When the ship is not         turning, the rate of turn is zero, and thus the list does not         have an effect on the penalty function.

In the preferred embodiment the present invention is implemented as computer software that is installed in a steering system that is modified to fulfill the needs of the present invention. In addition to the means for software execution, the steering system needs to be able to receive correct orientation data from steering devices and the delivered power in each orientation. The steering system must also be able to adjust the orientation of each steering device in accordance with the selected optimum.

In an embodiment of the invention the computer program mentioned above is embodied in a computer readable medium. The computer program embodied in the computer readable medium is executed in the marine vessel. Thus, a person skilled in the art understands that the marine vessel incorporates computing means that are capable of executing computer programs and giving instructions to controllers controlling the steering system and steering devices.

It is obvious to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways. The invention and its embodiments are thus not limited to the examples described above; instead they may vary within the scope of the claims. 

1-15. (canceled)
 16. A method for controlling a steering system of a marine vessel having at least two steering devices, which method comprises: acquiring data from the steering system of a marine vessel by changing the orientation of each steering device so that the steering angle of the marine vessel is maintained, creating a statistical model from said acquired data; and, selecting optimum values for orientation of each steering device based on the created statistical model.
 17. A method according to claim 16, wherein the method further comprises preprocessing said acquired data.
 18. A method according to claim 16, wherein the method further comprises a step of actuating the steering devices according to said selected optimum values during same journey.
 19. A method according to claim 16, wherein the acquired data comprises data relating to the fuel efficiency.
 20. A method according to claim 16, wherein the preprocessing of the acquired data further comprises filtering said acquired data, wherein said filtered data is limited to the data relating to at least one predetermined physical phenomenon.
 21. A method according to claim 16, wherein said statistical model is created by using at least one of the following machine learning methods: neural networks, Bayesian regression, or least squares regression.
 22. A method according to claim 16, wherein the method is performed by a computer program executed in a computing device.
 23. A method for controlling a steering system of a marine vessel having at least two steering devices, which method comprises the steps of: acquiring data from the steering system of a marine vessel by changing the orientation of each steering device so that the steering angle of the marine vessel is maintained; sending said acquired data to a remote server; and receiving optimum values for orientation of each steering device from said remote server.
 24. A method according to claim 23, wherein the method further comprises a step of actuating the steering devices according to said selected optimum values during same journey.
 25. A method according to claim 23, wherein the method is performed by a computer program executed in a computing device.
 26. A steering system for a marine vessel comprising at least two steering devices and a controller for controlling the steering devices, wherein the steering system is configured to: acquire data from the steering system of a marine vessel by changing the orientation of each steering device so that the steering angle of the marine vessel is maintained, create a statistical model from said acquired data; and, select optimum values for orientation of each steering device based on the created statistical model.
 27. A steering system for a marine vessel according to claim 26, wherein the steering system further comprises a computing device, wherein the computing device is configured to perform said acquiring, creating and selecting by executing a computer program.
 28. A steering system for a marine vessel according to claim 26, wherein said steering system is comprised in said marine vessel.
 29. A steering system for a marine vessel according to claim 28, wherein said steering devices are rudders or azimuth thrusters.
 30. A steering system for a marine vessel comprising: at least two steering devices; a controller for controlling the steering devices; and data communication means, wherein the steering system is configured to: acquire data from the steering system of a marine vessel by changing the orientation of each steering device so that the steering angle of the marine vessel is maintained; send said acquired data to a remote server; and receive optimum values for orientation of each steering device from said remote server.
 31. A steering system for a marine vessel according to claim 30, wherein the steering system further comprises a computing device, wherein the computing device is configured to perform said acquiring, sending and receiving by executing a computer program.
 32. A steering system for a marine vessel according to claim 30, wherein said steering system is comprised in said marine vessel.
 33. A steering system for a marine vessel according to claim 32, wherein said steering devices are rudders or azimuth thrusters. 